JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2009

  • question_answer
        If\[A=\left[ \begin{matrix}    \alpha  & 0  \\    1 & 1  \\ \end{matrix} \right]\]and\[B=\left[ \begin{matrix}    1 & 0  \\    5 & 1  \\ \end{matrix} \right],\]then value of a for which\[{{A}^{2}}=B\]is

    A)  1                                            

    B) \[-1\]

    C)  4                                            

    D)  no real value

    Correct Answer: D

    Solution :

                     Given, \[A=\left[ \begin{matrix}    \alpha  & 0  \\    1 & 1  \\ \end{matrix} \right],B=\left[ \begin{matrix}    1 & 0  \\    5 & 1  \\ \end{matrix} \right]\]and\[{{A}^{2}}=B\] \[\Rightarrow \]               \[{{A}^{2}}=\left[ \begin{matrix}    \alpha  & 0  \\    1 & 1  \\ \end{matrix} \right]\left[ \begin{matrix}    \alpha  & 0  \\    1 & 1  \\ \end{matrix} \right]=\left[ \begin{matrix}    {{\alpha }^{2}} & 0  \\    \alpha +1 & 1  \\ \end{matrix} \right]\] \[\because \]     \[{{A}^{2}}=B\] \[\Rightarrow \]               \[\left[ \begin{matrix}    {{\alpha }^{2}} & 0  \\    \alpha +1 & 1  \\ \end{matrix} \right]=\left[ \begin{matrix}    1 & 0  \\    5 & 1  \\ \end{matrix} \right]\] \[\Rightarrow \]               \[{{\alpha }^{2}}=1\]and\[\alpha +1=5\] Which is not possible at the same time. \[\therefore \]No real value of a exist.


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